This invention relates to new and useful improvements in ventilating systems for dryers of the type which utilize heat and circulating air means in combination. The invention in particular relates to a system capable of recovering waste heat from an exhaust air stream and transferring it to a make-up stream of air entering the dryer.
Various types of ventilating systems have been used in dryers which cure articles such as lumber kilns, fruit dryers, and the like. These ventilating systems comprise essentially means for heating the interior of the dryer, circulating means, outlet means for discharging moisture laden air, and means for drawing in make-up air. These prior systems have some inherent disadvantages. For example, the moisture laden heated air is discharged directly into atmosphere which comprises a waste of valuable energy. Also, the incoming air must be heated to accomplish the desired drying and pickup of moisture and this requires considerable energy for bringing the make-up air to its working temperature. These conditions lead to a more expensive operation in view of the energy required for heating. Also, the opening of roof vents in present day dryers decreases the pressure in the dryer and this in turn causes a velocity drop across the load as well as allowing inefficient escape of make-air.